The present invention relates to a wire bonding method used for producing a semiconductor device.
The wire bonding method has been used for connecting an electrode pad on a semiconductor chip and an inner lead of a lead frame through metal wires having a diameter of 20-30 .mu.m, such as gold wire or aluminum wire.
Heat pressure welding, ultrasonic bonding, and the combination of heat pressure welding and ultrasonic bonding have been adopted in the wire bonding method.
Heat pressure welding is the method where the clean surfaces of both metal materials are pressed below the melting points of the two metal materials, so that the bonding of both the metal materials is performed not by the melting of the metal materials but by the diffusion of the metal materials.
Ultrasonic bonding is the method where ultrasonic oscillation is transmitted to the metal wire, and the metal wire is pressed against the electrode pad made of aluminum, for example, and after that, the bonding is performed by the friction heat occurring between the electrode pad and the metal wire.
The inner lead and the electrode pad are connected by a metal wire forming a loop. When the height of the loop is low, the metal wire comes into contact with the semiconductor chip, and therefore problems of short circuiting may occur.
In order to prevent problems of short-circuiting, a capillary holding the metal wire is operated in a manner such that the capillary is horizontally moved (reversed) at a predetermined level while raising the capillary.
In the conventional wire bonding method, operators change the amount of reverse of the capillary every time the shape of the loop varies according to the height difference between the electrode pad and the inner lead.
However, it is difficult to precisely and quickly change the reverse movement amount of the capillary because the operator changes it by watching the shape of the loop. This has been a problem in a quality control.